Remanence Loss Research Articles

Electroless Ni-Co-P Coatings on Sintered Nd-Fe-B Magnets with Improved Corrosion Resistance

Electroless Ni-Co-P coatings have been deposited on sintered Nd-Fe-B permanent magnets by optimizing the bath composition and operating conditions. The corrosion resistance of coated Nd-Fe-B magnets was significantly improved and corresponding corrosion current density Icorr in 3.5 wt. % NaCl solution decreased by two orders of magnitude. Coated with 12μm-thick Ni-Co-P, Nd-Fe-B magnets possessed slight reduction in magnetic properties, with a modest loss of remanence (Br) by 3.9 % and coercivity (iHC) by 4.5 %.

Low‐temperature magnetic properties of greigite (Fe3S4)

We provide comprehensive low‐temperature magnetic results for greigite (Fe3S4) across the spectrum from superparamagnetic (SP) to multidomain (MD) behavior. It is well known that greigite has no low‐temperature magnetic transitions, but we also document that it has strong domain‐state dependence of magnetic properties at low temperatures. Blocking of SP grains and increasing thermal stability with decreasing temperature is apparent in many magnetic measurements. Thermally stable single‐domain greigite undergoes little change in magnetic properties below room temperature. For pseudo‐single‐domain (PSD)/MD greigite, hysteresis properties and first‐order reversal curve diagrams exhibit minor changes at low temperatures, while remanence continuously demagnetizes because of progressive domain wall unpinning. The low‐temperature demagnetization is grain size dependent for PSD/MD greigite, with coarser grains undergoing larger remanence loss. AC susceptibility measurements indicate consistent blocking temperatures (TB) for all synthetic and natural greigite samples, which are probably associated with surficial oxidation. Low‐temperature magnetic analysis provides much more information about magnetic mineralogy and domain state than room temperature measurements and enables discrimination of individual components within mixed magnetic mineral assemblages. Low‐temperature rock magnetometry is therefore a useful tool for studying magnetic mineralogy and granulometry of greigite‐bearing sediments.

Mineral magnetic signatures in a long core from Lake Qarun, Middle Egypt

The analysis and interpretation of changes in mineral magnetic signatures from a long (ca. 8.2 m) sedimentary sequence recovered from Lake Qarun, Middle Egypt in 2003 spanning a timescale of approximately the last 2,000 years is reported. A suite of mass specific susceptibility and magnetic remanence measurements were made at irregular intervals downcore on 39 samples. These samples were selected on the basis of trends and abrupt changes in whole-core magnetic susceptibility measured using a Bartington® MS2E sensor and were analysed for low and high temperature loss on ignition and their particle size distribution. Trends in all mineral magnetic concentration parameters are remarkably similar and were initially used to divide the core into three magnetically distinct zones. The upper and lower sections of the core (0–119 cm and 445–822 cm depth) are characterised by low values for all magnetic concentration parameters. Between 153 and 380 cm depth, concentration parameters are considerably higher, although somewhat variable. The S ratio and percentage loss of remanence after 24 h (IRMloss) follow a different trend and are inversely related to each other. A low S ratio ( 4%. On the basis of these parameters, the core can be divided into four zones, and differences in magnetic mineralogy between these four zones were confirmed by measurement of IRM acquisition curves. The major difference between concentration parameters and ratios or percentage loss of IRM lies in the identification of an additional zone below 619 cm depth where the S ratio is high and IRMloss is low. There is little evidence to suggest that the magnetic signatures are controlled by particle size or by trends in organic matter and/or carbonate content. The signatures appear to be predominantly detrital and show little evidence of post-depositional alteration through dissolution or authigenic addition of bacterial magnetite or greigite. Analysis of Saharan dust deposition rates in Northern Egypt suggests that atmospheric fallout is likely to make only a very minor contribution (<1%) to sedimentation rates in Lake Qarun. The downcore trends therefore appear to reflect major changes in fluvial sediment sources over the ca. 2,000 year time period spanned by this ∼8 m core. Preliminary mineral magnetic characterisations of potential local sources suggest that these cannot account for the range of signatures recorded in the Qarun sediments and it is hypothesised that these sediments are derived from Nile river floods.

Low-temperature partial magnetic self-reversal in marine sediments by magnetostatic interaction of titanomagnetite and titanohematite intergrowths

With various low-temperature experiments performed on magnetic mineral extracts of marine sedimentary deposits from the Argentine continental slope near the Rio de la Plata estuary, a so far unreported style of partial magnetic self-reversal has been detected. In these sediments the sulphate-methane transition (SMT) zone is situated at depths between 4 and 8 m, where reductive diagenesis severely alters the magnetic mineral assemblage. Throughout the sediment column magnetite and ilmenite are present together with titanomagnetite and titanohematite of varying compositions. In the SMT zone (titano-)magnetite only occurs as inclusions in a siliceous matrix and as intergrowths with lamellar ilmenite and titanium-rich titanohematite, originating from high temperature deuteric oxidation within the volcanic host rocks. These abundant structures were visualized by scanning electron microscopy and analysed by energy dispersive spectroscopy. Warming of field-cooled and zero-field-cooled low-temperature saturation remanence displays magnetic phase transitions of titanium-rich titanohematite below 50 K and the Verwey transition of magnetite. A prominent irreversible decline characterizes zero-field cooling of room temperature saturation remanence. It typically sets out at ∼210 K and is most clearly developed in the lower part of the SMT zone, where low-temperature hysteresis measurements identified ∼210 K as the blocking temperature range of a titanohematite phase with a Curie temperature of around 240 K. The mechanism responsible for the marked loss of remanence is, therefore, sought in partial magnetic self-reversal by magnetostatic interaction of (titano-)magnetite and titanohematite. When titanohematite becomes ferrimagnetic upon cooling, its spontaneous magnetic moments order antiparallel to the (titano-)magnetite remanence causing an drastic initial decrease of global magnetization. The loss of remanence during subsequent further cooling appears to result from two combined effects (1) magnetic interaction between the two phases by which the (titano-)magnetite domain structure is substantially modified and (2) low-temperature demagnetization of (titano-)magnetite due to decreasing magnetocrystalline anisotropy. The depletion of titanomagnetite and superior preservation of titanohematite is characteristic for strongly reducing sedimentary environments. Typical residuals of magnetic mineral assemblages derived from basaltic volcanics will be intergrowths of titanohematite lamellae with titanomagnetite relics. Low-temperature remanence cycling is, therefore, proposed as a diagnostic method to magnetically characterize such alteration (palaeo-)environments. © 2007 The Authors Journal compilation © 2007 RAS.

Characterization of the structural and magnetic properties of Nd16Co76-xRu xC7B alloys

The Nd16Co76-xRu xC7B system has been investigated to assess the effect of boron-carbon combined addition on the ferromagnetic behavior of these intermetallic compounds. The results indicate that the addition of 1 at.% B favors the formation of the tetragonal magnetic phase 2:14:1 in these alloys. With the increase of the Ru concentration is observed an expansion of the lattice in the basal plane as well as a contraction along the c direction of the tetragonal unit cell. The Curie temperature decreases from 432 K at x = 6 to 421 K for x = 27, whereas the saturation magnetization has a steep decrease. The highest T C value has been verified for the alloy with the largest c parameter, despite its a parameter is the smallest one. In comparison to isotypic borides and pure carbides, a loss of coercivity and remanence is observed.

Magnetic memory and coupling between spin‐canted and defect magnetism in hematite

Saturation isothermal remanent magnetization (SIRM) has been studied on submicron hematite powders with grain sizes between 0.12 and 0.52 μm and on 2 to 5 mm natural hematite single crystals before and after zero‐field cycling through the Morin transition (TM). SIRM cooling and warming curves for single‐domain (SD) crystals are similar to those of multidomain (MD) hematites. Both have similar remanence losses at TM (97–98% of the original SIRM), a similar defect moment below TM (2–3% of initial SIRM), and similar memory (30–40% of initial SIRM). Regardless of grain size, higher SIRM memory ratios are associated with higher defect moments below TM. In SD and MD hematites alike, room temperature magnetic memory seems to be an amplification of residual weak ferromagnetism that persists even at very low temperatures, much below TM. Applying a strong field to initially demagnetized SD and MD hematites at 20 K produced a substantial SIRM, which spontaneously increased by a factor 10–28 upon crossing the transition at TM. These observations imply that some spins do not participate in the general rotation from the ferromagnetic c plane to the antiferromagnetic c axis below TM. The defect moment of these spins serves to restore preferred directions of spins and ferromagnetic domains during zero‐field warming through the Morin transition and is thus responsible for the memory phenomenon. The existence of a weak ferromagnetic moment in antiferromagnetic hematite below TM is also indicated by colloid patterns observed by Gallon. We propose that the mechanism of memory is clusters of spins pinned magnetoelastically by lattice defects. These spins rotate only partially out of the basal plane during cooling through TM. Some basal plane anisotropy, also magnetoelastic in origin, must remain below TM in order to explain the existence of low‐temperature SIRM and also to guide spin nuclei into preferred orientations above TM on rewarming through the transition in zero field.

The detection of bacterial magnetite in recent sediments of Lake Chiemsee (southern Germany)

The sediments of Lake Chiemsee, located in the Alpine foreland in Southern Germany, host a variety of magnetotactic bacteria (MTB), which contain intracellular crystals of magnetite arranged in linear chains. To detect bacterial magnetite in the carbonate-dominated surface sediments and further quantify its contribution to the magnetic signal of the sediments, we conducted detailed rock magnetic measurements as well as complimentary non-magnetic analyses (electron microscopy, powder X-ray diffraction, and sediment pore-water analysis). Our results demonstrate that biogenic single-domain magnetite (characterized by bullet- and truncated hexagonal prismatic shapes) is the dominant ferrimagnetic component in the topmost few centimetres of the sediment. The changes of magnetic properties with depth are due to the occurrence of live MTB and the downward increasing dissolution of biogenic magnetite. Moreover, the ratios of remanence loss on warming through the Verwey transition after field cooling and zero-field cooling of saturation isothermal remanence ( δ FC/ δ ZFC) were determined as 1.47 and 1.25 for freeze-dried and air-dried sediment samples containing MTB, respectively. These low ratios suggest that the bacterial magnetite chains were disrupted to a large extent and/or that the bacterial magnetosomes might have undergone partial low-temperature oxidation. It is proposed that although rock magnetic measurements are suitable for quantifying the contribution of fine-grained particles to the overall magnetic signal of sediments, complementary non-magnetic methods are essential to unambiguously identify its bacterial origin.

Multi-cycle low-temperature demagnetization (LTD) of multidomain Fe3O4 (magnetite)

An improved multi-cycle low-temperature demagnetization (MC-LTD) method for multidomain (MD) Fe3O4 (magnetite) by repeating LTD cycles between any two temperatures below 300K is proposed to provide more rigorous constraints on the utilization of the LTD mechanism. MC-LTD was performed for four temperature intervals, 300–150K, 150–125K, (cycling through the isotropic point Tk∼130K, where the first magnetocrystalline anisotropy constant K1 changes sign), 125–95K (cycling through the Verwey transition Tv∼120K, where crystal symmetry changes from cubic to monoclinic) and 95–60K. Results show that the remanence loss during MC-LTD depends on the number of LTD cycles. Above Tv, demagnetization of remanence after MC-LTD is caused by the gradual reorganization of magnetic domains. For the 95–125K interval, the remanence loss results from the changes of easy axes between [001] of the cubic phase above Tv and the c-axis of the monoclinic phase below Tv. These two processes approximately follow the Boltzmann-analog relation, but the latter involves more degree of freedom. Below Tv, thermal equilibrium processes control the minor decay (less than 0.5% of the initial remanence intensity) of remanences.

More on the low‐temperature magnetism of stable single domain magnetite: Reversibility and non‐stoichiometry

The loss in remanence at the Verwey transition (TV) was modeled for elongate stable single domain magnetite for two experiments: 1) thermal cycling of room temperature saturation isothermal remanent magnetization (RTSIRM), 300 → 10 → 300 K, and 2) warming of zero‐field cooled and field‐cooled remanences from 10 K to 300 K. The RTSIRM simulations used magnetocrystalline anisotropy constants for stoichiometric magnetite and aspect ratios (AR) from 1 to ∞, for assemblages of inorganic particles and 10‐magnetosome chains. The results match the experimentally observed behavior of reversibility. The second set of simulations was conducted with low‐temperature magnetocrystalline anisotropy constants for varying degrees of non‐stoichiometry, and AR = 5. Minor non‐stoichiometry lowers the drop in remanence at TV and increases the “delta ratio” (δfc/δzfc) to values as high as ∼6. New experiments demonstrate that maghematization (non‐stoichiometry) can partly explain the low‐temperature magnetic behavior observed in magnetotactic magnetite to date.

Low‐temperature magnetic properties of lepidocrocite

The magnetic properties of synthetic lepidocrocite (γ‐FeOOH) were investigated between 5 and 300 K. The purity of the samples was verified by X‐ray diffraction and Mössbauer spectra at room temperature. The lepidocrocite is paramagnetic at room temperature with a low field susceptibility of 57.8 × 10−8 m3 kg−1. It undergoes magnetic ordering at low temperature and a peak in in‐phase susceptibility occurs around 52 K, where it is antiferromagnetic. Thermal demagnetization of low‐temperature remanence after cooling in zero field and in a 2.5‐T field display a large loss in remanence from 5 to 30 K. Hysteresis loops are open and symmetric about the origin below 50 K; the remanent magnetization probably arises from a defect magnetic moment. The field‐cooled hysteresis loop at 5 K is shifted along the field axis, which implies an exchange bias between antiferromagnetic and ferrimagnetic alignment in the lepidocrocite.

Induced remanent magnetization of social insects

The induced remanent magnetization (IRM) of honeybees Apis mellifera and ants as Pachycondyla marginata, a migratory species, and Solenopsis sp., a fire ant, was obtained using a SQUID magnetometer from 10 to 300 K. An anomalous sharp change of the remanent magnetization is observed at 67±0.2 K for migratory ants. The IRM at room temperature indicates the presence of at least 10 times lower concentration of magnetic material in the whole fire ant as compared to the migratory ant abdomen (0.22±0.33×10 −6 emu/ant, and 2.8±1.2×10 −6 emu/abdomen, respectively). Our results in honeybee abdomen (4.6±0.9×10 −6 emu/abdomen) agree with other reported values. IRM at room temperature in ants and honeybees indicates the presence of single domain (SD) or aggregates of magnetite nanoparticles. The loss of remanence from 77 to 300 K can be related to the stable-superparamagnetic (SPM) transition of small particles (less than ca. 30 nm). From these values and considering their estimated volumes an upper limit 10 10 SPM and 10 9 SD or aggregate particles are obtained in these insects.

Finite element modeling of nanocomposite magnets

Finite element modeling treats magnetization processes within the framework of micromagnetic theory, taking into account the complex microstructure of a magnet. The numerical integration of the Gilbert equation of motion provides the time evolution of the magnetization and thus shows how reversed domains nucleate and expand. The numerical results of static micromagnetic calculations reveal the influence of the intrinsic magnetic properties on the remanence and the coercive field of nanocomposite Nd/sub 2/Fe/sub 14/B//spl alpha/-Fe/Fe/sub 3/B magnets. An increase of the hard phase anisotropy of only 8% increases the coercive field from 340 kA/m to 450 kA/m in two phase Nd/sub 2/Fe/sub 14/B//spl alpha/-Fe magnets. This effect becomes less pronounced with increasing Fe/sub 3/B content. In two phase Nd/sub 2/Fe/sub 14/B/Fe/sub 3/B, the reduction of the soft phase magnetization and/or the soft phase exchange constant leads to an improvement of the coercive field without a significant loss in remanence. The magnetostatic interactions between the magnetic particles of bonded, nanocomposite magnets slightly reduce the remanence and the coercive field.

Rare earth magnets resisting eddy currents

Magnets with high electrical resistance were prepared by electrically isolating Sm/sub 2/Co/sub 17/ and Nd/sub 2/Fe/sub 14/B powder particles. This is achieved by a polymer mixture consisting of epoxy polyester-insulant (EPI), polyvinylbutyral (PVB), epoxy resin (ER) and silane coupling (SC). The properties of interest for anisotropic Sm/sub 2/Co/sub 17/ and isotropic Nd/sub 2/Fe/sub 14/B magnets respectively are /spl rho/=1/spl times/10/sup 5/ /spl Omega/-cm/sup 2//m, Br=6.8 kG, iHc=10.0 kOe, (BH)max=9.2 MGOe in 5%EPI, 4%PVB, 2%ER, 1%SC and /spl rho/=9.4/spl times/10/sup 4/ /spl Omega/-cm/sup 2//m, Br=4.5 kG, iHc=9.5 kOe, (BH)max=13 MGOe in 4%EPI, 3%PVB, 2%ER, 1%SC. The insulated magnets exhibit far better magnetic stability than those of sintered and bonded magnets after magnetizing in radio frequency field. The insulated Sm/sub 2/Co/sub 17/ magnet has the best performance in resisting eddy current. At 500 kHz frequency, 830 Oe magnetizing-field and in one minute, the irreversible loss of recoil remanence is 1.47% and 22.2% respectively for insulated Sm/sub 2/Co/sub 17/ and Nd/sub 2/Fe/sub 14/B magnets.

Micromagnetics of Nanocrystalline Permanent Magnets

ABSTRACTMicromagnetic finite element calculations provide the theoretical limits for the remanence, the coercive field, and the coercive squareness of nanocomposite Nd2Fe14B/α-Fe,Fe3B,Fe23B6magnets. The influence of the intrinsic magnetic properties and the microstructure were investigated using an energy minimization technique. The coercive field reaches a maximum as a function of the average grain size at about 15 nm - 20 nm. The replacement of α-Fe with Fe3B improves the coercive field but deteriorates the loop shape. The reduction of the magnetization and the exchange constant in the soft magnetic Fe3B phase by 20% improves the coercive field without a significant loss in the remanence. An increase of the hard phase anisotropy by 8% enhances the coercive field by more the 100 kA/m in two-phase α-Fe/Nd2Fe14B and by 60 kA/m in two-phase Fe3B/Nd2Fe14B magnets. Dynamic simulations for magnetostatically interacting particles of a bonded magnet show a slight influence of the particle arrangement on magnetization reversal. The interaction field in the range of 100 kA/m to 200 kA/m rapidly decreases the distance from the particle.

Modeling of hysteresis in magnetic cores with frequency-dependent losses

A novel hysteresis model is presented which exhibits all main features of hysteresis, such as initial magnetization, saturation, coercivity, remanence and frequency-dependent losses. It consists merely of three differential equations with six parameters. Depending on the slope of the outer hysteresis loop four variants of the model are discussed.

Low-temperature demagnetization of saturation remanence in magnetite-bearing dolerites of high coercivity

We studied 16 magnetite-bearing dolerite dyke samples of high coercive force (HC ranging from 11 to 50 mT) that had been used successfully in Precambrian palaeomagnetic studies. Each dolerite was given a saturation remanent magnetization, whose change was measured as the sample was cooled to 77 K in zero field and warmed back to room temperature. Only the three dolerites of highest HC (µ40 mT) show little change on cooling, suggesting that their magnetite is mostly in elongated single-domain grains. The rest of the dolerites are likely to be dominated by pseudosingle-domain magnetite. Cooling to ~135 K causes their remanence to decrease (by 37 per cent on average) in rough proportion to the decrease in saturation magnetostriction, as expected if internal stresses oppose domain wall motion. Cooling from~135 K to 77 K causes remanence to decrease further (by 26 per cent on average), probably mostly because of domain reorganization forced by magnetite’s Verwey crystallographic transition. Warming back to room temperature causes some of the remanence loss to be recovered, perhaps because internal stresses act as a bridge between different easy axes below the Verwey temperature (~122 K) and above the isotropic point (~135 K). This recoverable low-temperature demagnetization averages 23±6 per cent of the initial saturation remanence, while the permanent demagnetization averages 40±9 per cent. Recoverable low-temperature demagnetization is even larger for natural remanence, averaging 46±9 per cent for the six dolerites measured, while the corresponding permanent demagnetization averages 13±6 per cent. Large recoverable low-temperature demagnetization seems to be characteristic of pseudosingle-domain magnetite in which high internal stresses block domain-wall motion, and may be common in mafic igneous rocks like our dolerite samples, whose magnetite is intergrown with ilmenite lamellae. Measuring natural remanence of such rocks before, after and while at 77 K should help separate remanence carried by multidomain magnetite (mostly permanently demagnetized), by single-domain magnetite (mostly unchanged) and by pseudo-single-domain magnetite (mostly responsible for recoverable demagnetization).

Low‐temperature magnetic properties of siderite and magnetite in marine sediments

Low temperature magnetic techniques provide useful tools to detect the presence of magnetite and pyrrhotite in sediments through identification of their low temperature transitions, to determine the amount of ultrafine‐grained (superparamagnetic) material in sediments, and can potentially detect the presence of certain types of magnetotactic bacteria. Application of these types of experiments to nannofossil chalks from beneath the Barbados accretionary prism led to some unusual results, which are attributed to the presence of siderite. Thermal demagnetization of low‐temperature remanence after cooling in zero field and in a 2.5 T field both displayed large remanence losses from 20 K to 40 K. Below 40 K, the magnetization of the chalks was much higher in the field‐cooled experiments than in the zero‐field‐cooled experiments. Low temperature hysteresis experiments, made after cooling in a 2.5 T field, displayed offsets in magnetization parallel to the direction of the initial applied field, when measured below 40 K. The offset loops can be due to either an exchange anisotropy between siderite and magnetite phases in the sediments, a defect moment in the siderites, or a canted moment in the siderites. Apparent similarity between the low‐temperature thermal demagnetization results from these siderite‐bearing sediments, pure siderite, and pure rhodochrosite samples and the well‐known 34 K transition in pyrrhotite should lead to caution in identification of pyrrhotite in marine sediments based on low‐temperature remanence studies alone.

Effect of gallium additions on the magnetic properties of die-upset forged Fe-Nd-B type melt spun alloys

The magnetic properties of melt spun ribbon, hot pressed and die-upset forged Fe79 − xNd15B6Gax (x = 0–1.5 at%) magnets have been investigated. It has been found that Ga additions up to 1 at% significantly increase the coercivity of the Fe-Nd-B alloys but further additions cause a dramatic decrease in coercivity. Gallium contents to 1 at% do not influence the Curie temperature of the magnets although the melting point of the grain boundary Nd-rich phase is significantly reduced. The optimum properties for the die-upset magnet have been established at 0.25 at% Ga whereby a 25% increase in coercivity has been observed with little loss in remanence and energy product. We attributed the initial changes in the magnetic properties of Fe-Nd-B dieupset forged magnets containing Ga to the reduction of the melting temperature of the boundary phase resulting in better magnetic isolation of the hard magnetic grains and the pinning effect of the precipitates of Ga-rich phases.

Relative palaeointensity records from the Ontong-Java Plateau

SUMMARY Rock magnetic, palaeomagnetic and oxygen isotopic results are presented from core RNDB 75p, which was recovered from the Ontong-Java Plateau (OJP). A high degree of uniformity in magnetic properties characterized by relatively small changes in concentration and grain size in the upper 4 m of the core, combined with a lack of coherence between the normalized remanence and rock magnetic data suggests that the natural remanence normalized by saturation remanence reflects variations in relative palaeointensity of the geomagnetic field. The record from RNDB 75p replicates other Ontong-Java records spanning the last 400Ka and extends the record back to some 700Ka. Spectral analysis of the Ontong-Java record suggests periodic behaviour in the relative palaeointensity record with a dominant period of between 30 and 40Ka, which appears not be be an artefact of lithologic variability. This dominant period lies between functions describing climatic precession and obliquity changes in the Earth’s orbit. Comparison of the normalized remanence record with astronomical precession (26 Ka period), however, is much more favorable. None the less, ‘tuning’ the palaeointensity record to that of astronomical precession appears inconsistent with existing isotopic age constraints derived from the SPECMAP time-scale. Based on these data, we must choose between assuming that the Earth’s orbit controlled ice volume (inherent in the SPECMAP time-scale) and assuming that the Earth’s magnetic field is driven by astronomical precession. The former assumption has a substantial theoretical and observational base and we prefer to interpret the data presented here as suggesting that the Earth’s orbit has not played a detectable role in the modulation of the magnetic field. Plots of saturation remanence and magnetic susceptibility are very sensitive to quite subtle changes in magnetic grain size. A slight shift within the pseudo-singledomain grain-size range toward the multidomain (or superparamagnetic) field was detected at about 4m in RNDB 75p. This change in grain size may reflect a diagenetic alteration of the magnetite (such as dissolution) and may be related to the phenomenon responsible for the loss of magnetic remanence at depth detected in other cores from the region.

Angular dependent recording behavior of ME tape

The recording behavior of metal evaporated (ME) tape as a function of the angle between the direction of recording and the usual running direction of the tape is investigated in detail. It is found that the output-vs-angle curves exhibit a shift and a narrowing of the peak centered at about the normal recording direction as well as a broadening of the peak centered at the opposite direction. This is explained by a combination of remanence loss effects and the relevant head field gradients at the wiring point.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>